The manufacture of polynitrotoluene compounds for munitions and explosives is a major industry. Large production requirements and the broad variety of manufactured products lead to significant pollution problems, however. One of the most serious of these is waste waters which are generated during the manufacture of explosive polynitrotoluene compounds, such as trinitrotoluene (TNT), including 2,4,6-trinitrotoluene (.alpha.-TNT).
During manufacture, such compounds are subjected to a finishing process wherein the end product is dried, flaked and packaged. After manufacture, the production equipment and neighboring areas of the facilities housing such equipment are ordinarily rinsed thoroughly or washed down with water to clean away any residues of TNT which have been left behind. This cleaning procedure typically involves the use of considerable amounts of water, e.g., up to 500,000 gallons per day at a single site, and the resulting water wash is commonly discharged into nearby rivers or streams. The discharge of this water presents a major pollution problem. It has been found, for instance, that as little as 2.5 parts per million (ppm) of TNT is toxic to fish, while the concentration of TNT in industrial discharges is considerably higher, e.g., 50 ppm or more.
Extensive studies of the treatment of industrial waste waters from the manufacture of TNT have been conducted by various academic institutions, defense laboratories, private industries, and others. Methods investigated so far include bacterial degradation, carbon-adsorption techniques, irradiationdecomposition and adsorption on organic resins. These are described in the article, "Application of Liquid Chromatography to Pollution Abatement Studies of Munition Wastes", by Walsh et al, ANALYTICAL CHEMISTRY, Vol. 45, No. 7, June 1973, pages 1215-1220, and the references cited therein, incorporated herein by reference. At the present time, carbon adsorption enjoys the widest use in industrial waste treatment processes to remove TNT. In general, this technique involves contacting TNT-containing waste water with activated charcoal or an activated carbon meterial, e.g., Filtrasorb-400 (Calgon Corp., Pitts., Pa.), which results in the adsorption of TNT and its colored decomposition species on the activated adsorbent material. Carbon adsorption has several disadvantages which limit its use, however. For instance, even after the TNT has been adsorbed it remains explosive and highly dangerous, especially when dry. As a result, regeneration of the carbon material for further use, which is ordinarily carried out in the case of other pollutants by burning the activated carbon material to oxidize the adsorbed pollutants, can not be accomplished with reasonable safety when TNT is the adsorbed material. Moreover, as a result of the afore-mentioned carbon regeneration difficulties, the spent carbon adsorbent must usually be discarded and replaced with fresh amounts, which is a costly procedure.
Other methods involve extraction of the TNT from water by the use of water immiscible organic solvents, e.g., toluene. Significant amounts of TNT remain behind in the water layer even with extraction, however, and further waste treatment is required. Such further treatment often involves the use of the afore-mentioned carbon adsorption methods with their attendant disadvantages. Thus, there remains a widespread need for a method of removing TNT safely and efficiently from industrial discharges.
The present invention provides a simple, safe and low cost method of removing TNT from waste water. The method is based on the surprising discovery that certain amino group containing compounds alone or together with cationic compounds cause the formation of water-insoluble reaction products with TNT. The resulting precipitates can be readily and safely removed and the treated waste water can then be safely discharged or further treated to remove other pollutants, without hazard, by conventional methods.